The present invention relates in general to active antenna systems for radio receivers, and, more specifically, to a power interface for an active antenna including fault diagnostics and protection.
Powered antenna systems for radio receivers are often used in order to boost an antenna signal from an external antenna (i.e., an antenna not integrated into the receiver). A powered amplifier is located remotely with the antenna element and the amplified antenna signal is coupled to the receiver via an antenna feed, such as a coaxial cable. The amplification of the antenna signal avoids excessive signal degradation and loss that would occur during transmission from the antenna to the receiver.
In a mobile receiver system, such as an automotive radio receiver, it may be undesirable to provide an independent power supply having a main power feed at the antenna location. Therefore, a regulated power supply within the main radio receiver module (e.g., a head unit) may provide a DC voltage that is fed to an amplifier within a remote antenna module. In order to avoid any added conductor wires between the receiver and the antenna module, the DC power may be applied to the antenna feed itself. Highpass and lowpass filters are typically used to separate the DC voltage from the high frequency antenna signals at each end of the antenna feed.
An automotive application for which an active antenna is especially advantageous is a satellite radio receiver, such as for the Satellite Digital Audio Radio Service (S-DARS). A small S-band antenna module is typically mounted at the vehicle exterior, such as on a roof panel or a window glazing. A wire or cable installed between the S-DARS receiver and the antenna module courses through various body channels and cavities which may include various bends. If bent at too sharp an angle, a break may occur in the antenna signal line. Some body parts may be assembled after the antenna cable is put in place and the cable may be inadvertently pinched or otherwise damaged during assembly, which can lead to either open circuits (e.g., a break in the signal line) or a short circuit from the signal line to the vehicle body or between the signal line and the ground line (e.g., the shield conductor or a coaxial cable).
In the event of a fault in the antenna connection, it is desirable that the type of fault be automatically detected by the receiver and that there be a method for informing a service technician of the type of fault in order to facilitate repair of the fault. In the event of a short-circuit, the potential exists for damage to the radio receiver. Therefore, both fault detection and the ability to take protective action are desirable.
To improve cost and performance of radio receivers, their designs typically utilize the smallest electronic components possible. For example, in a satellite radio receiver, the RF tuner circuit may be miniaturized to the extent that leaded devices and even surface mount devices (SMD's) larger than an 0805 package style cannot be used. However, smaller sized components are more likely to be destroyed during a short-circuit condition. Consequently, it is desired that the circuitry for coupling a DC power input and for detecting fault conditions be implemented using SMD components of this smaller size while ensuring that the components will survive a short-circuit condition (e.g., until the short-circuit fault is detected and protective measures taken).